According to the prior art, multi-stage transmissions of a planetary design, in particular for motor vehicles, comprise planetary gear sets that are shifted using friction elements or shift elements such as clutches and brakes, and typically are connected to a start-up element, such as a hydrodynamic torque converter or a fluid coupling, that is subject to a slip effect and is provided optionally with a lock-up clutch.
Such a multi-stage transmission is known, for example, from the applicant's DE 199 49 507 A1, according to which two non-shiftable front-mounted gear sets are provided on the drive shaft that generate two rotational speeds on the output side and which, in addition to acting on the rotational speed of the drive shaft, can be selectively meshed with a shiftable double planetary gear set acting on the output shaft by selective engagement of the shift elements that are used such that only one of the two currently actuated shift elements must be engaged or disengaged to shift from one gear to the next higher or lower gear.
By using five shift elements, seven forward gears are obtained; by using six shift elements, nine or ten forward gears are obtained.
Furthermore, a nine-speed multi-stage transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four planetary gear sets, wherein one planetary gear set serves as a front-mounted gear set and the main gearing includes a Simpson set and a further planetary gear set serving as reverse gearing.
Further multi-stage transmissions are known, for example, from the applicant's DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1.
Automatically shiftable vehicle transmissions of a planetary design are already generally described numerous times in the prior art and are continually undergoing further development and improvement. As such, these transmissions should have a relatively simple design, in particular requiring a low number of shift elements, and minimize the need for double shifting, i.e. engaging and disengaging two shift elements, when sequential shifting is performed, thereby ensuring that only one shift element is ever switched when shifting is performed in defined groups of gears.
The applicant's document DE 10 2008 000 428 A1 discloses a multi-stage transmission of a planetary design that includes an input shaft and an output shaft which are disposed in a housing. The known transmission includes at least four planetary gear sets, which are designated in the following as the first, second, third, and fourth planetary gear sets, at least eight rotatable shafts, which are designated in the following as the drive shaft, output shaft, third, fourth, fifth, sixth, seventh, and eighth shafts, and at least six shift elements, comprising brakes and clutches, the selected engagement of which produces different transmission ratios between the input shaft and the output shaft, such that, preferably, nine forward gears and one reverse gear can be obtained.
The first and second planetary gear sets, which are preferably designed as minus planetary gear sets, i.e., having a negative stationary transmission ratio, form a shiftable front-mounted gear set, wherein the third and fourth planetary gear sets form a main gear set.
In the known multi-stage transmission, the carriers of the first and second planetary gear sets are coupled together via the fourth shaft, which is connected to an element of the main gear set, the ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set via the eighth shaft, which is detachably connectable to the drive shaft via a first clutch, and the sun gear of the first planetary gear set can be coupled, via a first brake, to a housing of the transmission by means of the third shaft, and is detachably connectable to the drive shaft via a second clutch, wherein the ring gear of the second planetary gear set can be coupled, via a second brake, to a housing of the transmission by means of the fifth shaft. In addition, the seventh shaft is permanently connected to at least one element of the main gear set, and can be coupled, via a third brake, to the housing of the transmission, wherein the sixth shaft is permanently connected to at least one further element of the main gear set and is detachably connectable via a third clutch to the drive shaft; the output shaft is permanently connected to at least one further element of the main gear set.
In the known transmission, the fourth shaft is preferably permanently connected to the ring gear of the third planetary gear set, wherein the sixth shaft is permanently connected to the ring gear of the fourth planetary gear set and to the carrier of the third planetary gear set, and is detachably connectable, via the third clutch, to the drive shaft. Furthermore, the seventh shaft is permanently connected to the sun gears of the third and fourth planetary gear sets, and can be coupled, via the third brake, to a housing of the transmission. In this case, the output drive is produced via the output shaft, which is permanently connected to the carrier of the fourth planetary gear set. Furthermore, the third and fourth planetary gear sets can be combined or reduced to a Ravigneaux set having a common carrier and a common ring gear.